Hydraulic pile driving hammer



y 1957 J. T. HAZAK ET AL 2,798,363

HYDRAULIC FILE DRIVING HAMMER Filed May 17, 1956 V 2 Sheets-Sheet 1 lINVENTORS. H I JoH/v THA ZA K 1 WILL. m M PiG/WVEMAN. I 1) BY ATTORNEYS.

July 9, 1957 HAZAK ET AL 2,798,363

. I HYDRAULIC FILE DRIVING HAMMER Filed May. 17, 1956 2 Sheets-Sheet 2jHOC/(AE- SURE/N6 HULA INVENTORS. Jon/v T HA ZAK. BY T WLL/AMPIGNNEMAM ATTORNEKS.

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HYDRAULIC PILE DRIVING HAMMER John T. Hazak, New York, N. Y., andWilliam P. Kinneman, Westfield, N. J., assignors to Raymond ConcretePile (Iompany, New York, N. Y., a corporation of New Jersey ApplicationMay 17, 1956, Serial No. 585,439

11 Claims. (Cl. 61-76) This invention relates to pile driving hammersand the like and more particularly to hydraulically operated hammers.

For many years, it has been the general practice to drive piles by theuse of steam hammers. Yet such steam hammers have a number of seriousdisadvantages. For example, the steam pressure which may in practice beused is generally limited to about 150 pounds per square inch, and withsuch relatively low pressures, in order to provide a differential pistonarrangement of such size as to operate a 5000 pound ram, for example,the upper piston must be of a diameter of nearly 14 inches, which isgenerally too large to permit the hammer to be fitted into the upper endof a pile driving core and thus substantial portions at least of thehammer must extend above such a core and this in turn minimizes theavailable headroom V in the pile driving assembly, which is an importantfactor in pile driving, particularly in the case of the driving of longpiles. The necessary piston size if steam is used, is also a limitingfactor in the case of hammers of types not to be contained in a pilecore and if, as is often desirable, very heavy rams are to be used. Forexample, to operate a ram of 15,000 pounds or heavier, the upper pistondiameter, if steam is used, must be about 24' or more. With a cylinderand piston of such sizes, difii- ,culty may be encountered in findingsufiicient space to ;support the hammer between the pile driver leads,unless :the latter and the supporting structure therefor are madeexcessively bulky and heavier than is the present practice. Anotherdisadvantage of steam hammers resides in the fact that the overallefficiency in the use of fuel, of the steam boiler and steam hammer, isvery low. Also the burning of fuel for the boiler creates a smokenuisance and fire hazard, and as the steam which escapes from the hammergenerally contains some oil, this creates a further nuisance as well asobjectionable noise.

Upon superficial consideration, it would appear that the abovedifficulties with steam hammers for the purpose could be overcome by theuse of hydraulic hammers, since by the use of hydraulics, operatingpressures of thousands of pounds are possible to be maintained by pumpsdriven with high efficiency from internal combustion engines, therebyavoiding the nuisances and losses of inefficient boilers and ofdischarging steam. Hydraulic pistons may be made quite small, even foroperating the heaviest rams, and small enough to mount the hammer downin the pile driving core or conveniently to suspend the hammer betweenthe leads of standard pile drivers, even though the ram used is muchheavier than heretofore generally attempted.

However, so far as is known, successful hydraulic pile driving hammershave not been heretofore developed or used and the use of hydraulics forthe purpose has involved difficulties which have not heretofore beensurmounted. Authoritative treatises on the use of hydraulic pistons formoving any large masses connected thereto have many times expressed acaution against any attempt to move the piston at a rate faster than twofeet per second, due to the destructive hydraulic shocks occuring whenthe valves and the direction of stroke are reversed. Such a speed ismuch too low for efficient pile driving. Experts in the art of hydraulicpistons also have long expressed caution against moving any large massesoperated by hydraulic pistons unless the assembly is decelerated atcontrolled rates such as to avoid hydraulic shock on the system andconsequent breakage of pipes, pumps and other components of the system.Like precautions have also long been taught against attemptinginstantaneously or practically instantaneously to stop the hydraulicpiston assemblies at the end of each stroke. It has also been thegeneral belief that it is impractical to directly couple a hydraulicpiston to a control valve to control its stroke because of thedifficulties of having the valve stop on dead center.

With the present invention, these long-recognized difiiculties ofhydraulically-operated piston and heavy mass assemblies are overcome bythe expedient of yieldably associating the hydraulic system with a heavyram, at least substantially at the time when the hydraulic piston isapproaching the end of its stroke, thereby permitting further travel ofthe ram and completion of its stroke in such a way that the stopping ofmovement of its heavy mass does not cause a destructive shock 'on thehydraulic system. This may be accomplished by yieldably connecting thepiston rod and ram as for example by a spring arrangement or otherresilient means compressible in the direction of the stroke. However,there are other possible expedients for attaining such yieldableassociation of the ram with the system, or for aiding in doing soconjointly with such a flexible connection. For example, the hydrauliccylinder may be yieldably mounted so that at the tenmination of thestroke of the piston in the cylinder, the piston will stop with respectto the cylinder and with respect to the body of liquid therein withoutundue shock to the system, even though the cylinder and piston assembly,being yieldably mounted, moves with the ram to completion of its stroke.Also means may be provided in effect to yieldably discharge liquid frombeneath the piston at the end of its stroke as by the use ofaccumulators of appropriate size, applied to the liquid intakeconnection to the cylinder, or by spring-release valves or other valvesoperable to be actuated at the end of the stroke to release liquid frombeneath the piston back to the source of liquid supply.

However, the expedient of using a yieldable connection between thepiston and ram, supplemented by the use of an accumulator, if desired,constitutes the presently preferred arrangement for the purpose. Such ayieldable connection in the form, for example, of a spring arrangement,may be so devised that when the piston for example approaches the end ofits down-stroke, the control valve acts abruptly to release thehydraulic pressure above the piston and since the hydraulic piston maybe relatively small and light, the piston itself can abruptly stop,whereas the ram, being resiliently attached thereto, is free to advancefurther to fully complete its stroke and apply the desired impact. Thecontrol valve for the piston is so actuated by means connected to theram, that such continued movement of the ram will insure completereversal of the control valve without danger of its stopping on deadcenter and thus insuring that the return stroke of the piston willpromptly start. Assuming that a differential type piston is used, thereturn or upward stroke of the piston itself can be abruptly stopped atthe desired moment by admitting hydraulic pressure again into the upperpart of the cylinder, whereas the ram being yieldably connected to thepiston, will be more gradually brought to a stop and its final upwardtravel will insure complete reversal again of the control valve to causeforceful and prompt starting of the next down-stroke.

Thus while the quite small lightweight hydraulic piston itself may bequite abruptly stopped at the end of each stroke, its weight isinsutficie'nt to cause destructive hydraulic shocks in the system and atthe same'time the ram, while very heavy, is only yieldably involved withthe hydraulic system and thus does not tend to cause any destructivehydraulic shocks therein.

In addition to the use of the above-explained spring connection betweenthe hydraulic piston and ram, the hydraulic intake connection to thecylinder may include a shock absorbing accumulator which will tendfurther to minimize the effects of any hydraulic shocks occurring at theends of the strokes of the piston ram assembly. In some cases in factsuch an accumulator may be used in lieu of the spring connection meansbetween the ram and piston, but ordinarily such spring connection isnecessary safely to achieve high speed operation of the hammer, and withsuch spring connection, satisfactory high speed operation may often bereadily achieved without such an accumulator.

Further and more specific objects, features and advantages of theinvention hereof will appear from the detailed description given belowtaken in connection with the accompanying drawings which form a part ofthis specification and illustrate, by way of example, preferredembodiments of the invention.

In the drawings:

Fig. 1 is a vertical sectional view showing one embodiment of ahydraulic hammer made in accordance with the invention and the upperportions of which are shown in Fig. 1a; portions of Fig. 1a being shownin section taken along line 1a1a of Fig. 2;

Fig. 2 is a horizontal sectional view taken substantially along line 22of Fig. 1a;

Fig. 3 is a vertical sectional view showing somewhat schematicallyanother hydraulic hammer in accordance with the invention and ascontained within the upper end of a pile driving core; and furthershowing a preferred arrangement of hydraulic pressure supplying andcontrol apparatus which may be used therewith and also with the type ofhammer shown in Figs. 1-2; and

Fig. 4 is an elevational view partly in broken section of a hammer as ofFig. 3 and contained in a core being used for driving a pile shell intothe earth.

-Referring'now to the drawings in further detail, the hammer as shown inFig. 1 comprises a hydraulic cylinder as at containing a differentialtypepiston 11 connected to a piston rod 12 and adapted to be operatedfor example by oil supplied at a pressure for example in theneighborhood of 2000 to 2500 pounds per square inch. The hammerram isshown at 13 slidably mounted upon column assemblies 14 which may be ofthe type disclosed in the-co-pending application of Edward A. Smith,Serial No. 544,225, filed November 1, 1955. The ramhas a point portion15 adapted to apply impacts to a cap block assembly indicated generallyat 16 and which, if desired, may be of a construction and arrangementsuch as shown in the patent to E. A. Smith, No. 2,723,532,'grantedNovember '15, 1955. The hammer base is indicated at 17, withsupplemental base parts 18 for receiving the cap block assembly, beneathwhich "may be located ball and socket means as at 19 such as disclosedin said Patent 2,723,532, for applying the impacts to a so-called hammerfollower indicated at 20.

A center plate may be provided as at 21 for retaining the lower end ofthe cylinder 10 in proper position with respect to the column means 14.A top plate forming a cylinder and valve support is indicated at 22.

' This embodiment of the invention, as will be apparent from Fig. 2, isadapted to be'slidably suspended between the followers or guide rails asat 23 of a pile driving hammer crane structure.

' The lower end of the piston rod 12,.as shown in Fig. 1, is connectedby threaded engagement with a hollow piston rod extension 24 which issurrounded by an'upper helical spring 25 and a lower and somewhatsmaller helical spring 26. The extension 24 has a flange portion 27secured thereto on its exterior and located between the adjacent ends ofthese two springs. The extension 24 is slidably retained in position bymember 28 which embraces same and is secured as by screws 29 to the ram13. The upper end of the extension 24 may be surrounded by a rubberbuffer member 30, which, at the end of each upstroke of the hammer, maystrike against the underside of the center plate 21. Spring washers suchas assemblies of Belleville washers or the like or other resilient meansare positioned as at 31, 32 above the upper end of spring 25 and belowthe lower end of spring 26. i

Suitable packing means as at 33 surrounds the piston rod at the lowerend of the cylinder and is contained within a central aperture in thecenter plate 21.

Hydraulic pressure is constantly maintained on the lower side ofpistonll and surrounding the piston rod 12 by a connection 34terminating at a port 36 opening into the lower end of the cylinder.Hydraulic pressure is applied to the upper face of the piston 11 duringeach down-stroke, through a connection 36 passing through the top plate22.

The piston 11, being arranged to operate as a differential piston, itwill be understood that the downstroke is caused by the hydraulicpressure against the upper face of the piston supplemented by the weightof the ram. While the hydraulic pressure will at the same time beapplied to the undersurface of the piston, yet the effective area ofsuch undersurface, due to the presence of the piston rod, is quite smallas compared with the effective area of the upper surface, andaccordingly the pressure under the piston does not act to prevent thedown-stroke. A valve is provided as hereinafter described which, atabout the timeof the starting of the upstroke, will relieve thehydraulic pressure against the upper face of the piston '11 so that thepressure beneath the piston will then be suflicient to raise the pistonand the attached ram. The piston on its upstroke acts to force theliquid above the piston back to the source of supply as will behereinafter explained more fully. Thus even if the hammer is located ata point far below the level of the hydraulic supply tank, it willoperate properly without any additional liquid return pump.

Referring now more particularly to Figs. 1a and 2, the incoming pressuresupply connection is shown at 37 and the liquid return connection isshown at 38. A reciprocating valve of suitable known type is containedwithin a valve chamber 40. Such valve may be constructed to operate inthe manner hereinafter further explained, for example, in connectionwith the embodiment of Fig. 3. Such a valve may be operated by areciprocable rod 41, which in turn is pivotally connected to a smallcrank 42 as'shown in Fig. 1a, this crank being mounted on a rockableshaft 43. Such shaft is adapted to be rocked by 'rockable trip members44 and 45 secured thereon. These trip members respectively are adaptedto be engaged by cam surfaces as at 44 and 45 formed on a valveoperating rod 46, which in turn is mounted on the ram 13 so that suchcam surfaces are reciprocated during each stroke of the hammer inaccordance with the movements of the ram. The rod 46 may be slidablyreceived in a guideway member 46' (Fig. 2).

A branch 34 from the pressure intake connection 37 runs down to thepressure connection 34 for maintaining the pressure beneath the pistonin the cylinder 10 at alltimes during operation of the hammer.

Theoperation of the hammer of Figs. 1-2 may be described as follows.First, we will assume that the piston is'in its uppermost position asshown and that the ram, acting through the cam means and one of the tripmembers, has just caused the valve in chamber 40 to move to a positionto admit hydraulic pressure to the upper surfaceof the piston. Thereuponthe down-stroke will start by reason of such pressure supplemented bythe weight of the ram and opposed somewhat by the hydraulic pressureconstantly maintained on the smaller and undersurface of the piston 11.The down-stroke will proceed until the ram has carried thevalve-operating cams down far enough so that the trip member 44 will beengaged and operated by the cam surface 44. Then the valve in chamber 40will be actuated to release abruptly the hydraulic pressure above thepiston and as soon as the upstroke starts, the liquid will be forcedfrom the cylinder space above the piston out through return connection38. While the release of the hydraulic pressure above the pistonsubstantially at the moment of termination of the down-stroke of thepiston, will cause the piston rather abruptly to stop its downwardmovement due to the pressure in under the piston, yet the ram, becauseof the presence of the spring 25, will not thus be abruptly stopped inits downward movement, but will be able to complete the impact of theram point against the cap block 16. The final downward movement of theram will insure movement of the control valve fully to its position forreleasing the pressure above the piston to the outlet connection 38.Also during the final downward movement of the ram, the spring will havebecome compressed somewhat and this will tend to cause the ram torebound, inasmuch as the spring will be reacting against the piston rodand at this moment, pressure under the piston will be tending to forcethe same upwardly and the upward movement of the ram will thus bepromptly and forcefully started and will continue until the pistonreaches a point near the upper end of its stroke. Meanwhile, thepressure under the piston will cause the piston forcibly to eject theliquid from above the piston out through the return connection 38 backto the hydraulic supply source.

As the piston approaches the upper end of its stroke, the cam and tripmembers will act to move the valve in the direction to close off thereturn connection 38 and to readmit the hydraulic pressure throughconnection 37 onto the upper surface of the piston. This will causeabrupt stopping of the upstroke of the piston, but the ram on the otherhand, due to the presence of spring 26, will be less rapidly deceleratedin its upward movement. And the ram will continue upwardly somewhatfurther and far enough to insure that the valve is completely opened topermit free admission of hydraulic pressure to the upper face of thepiston. Meanwhile, spring 26 will have become compressed somewhat andthus this :spring reacting against the now downwardly moving pis- .tonassembly, will tend rapidly to start the down-stroke of the ram, aidedby gravity, and such down-stroke will be powerfully continued by thehydraulic pressure above the piston.

Spring 25 when under compression tends to act against the force ofgravity on the ram and hence this spring should be relatively large.Spring 26, however, when under compression, tends to act with the aid ofgravity, and therefore this spring may be somewhat smaller. Spring 25should, of course, be large enough to support the weight of the ramduring the upstroke and also, in the event the impacts of the hammershould be against a pile in soft ground, then the spring 25 should beheavy enough to resist and stop execessive downward movement of the ramat the proper time. And if the impacts are applied against a pile suchthat the ram tends to rebound considerably, such rebound will beenhanced by the heavier spring 25 and thus cause more rapid starting ofthe upward stroke of the ram.

A hydraulic hammer of the example of the invention above described andwith a 5000 pound ram, has been found capable of delivering in theneighborhood of 110 blows per minute with a stroke of from 16 to 18inches. At this speed, the maximum velocity of the ram was about 13 feetper second, corresponding to over 13,000

foot pounds of delivered energy on each stroke. The cost of fuel foroperating the pump driving engine for such a hydraulic hammer amountsonly to some twentyfive percent or less of the fuel required foroperating such a steam hammer of equivalent size. The above-describedtype of hydraulic hammer is also particularly well adapted for use incases where much heavier rams are desirable as when a short strokehammer is preferred and in cases where only low headroom is available,necessitating a short stroke. And since oil may be used as the hydraulicliquid, the construction is well adapted for use where boiler water isnot easily obtainable or where low temperatures would be liable to causefreezing, of the water supply and water connections.

The form of the invention as shown in Figs. 3 and 4 somewhatschematically in the interests of simplicity, is embodied within theupper end of a pile driving core 50 such as may be used for driving forexample a tapered corrugated steel pile shell as at 51 (Fig. 4). Asindicated in Fig. 4, substantially all parts of this form of hammer,except for a sheave-supporting assembly 52 and the connection hoses, maybe located down below the upper end of the core. This is of greatadvantage as above noted, in that it makes possible greatly increasedheadroom, whereas in the prior steam hammer constructions, at least apart of the hammer, and more often all of it, because of the size of thepiston assembly, had to be located above the core. Thus the fact thatthe hydraulic hammer of this invention requires a piston assembly ofonly very small diameter, makes it possible to provide not only a muchmore compact and lighter arrangement, but also it should be noted thatthe hammer impacts will occur down substantially within the core, thusmuffiing to a large extent the sound of the impacts. The fact that thishydraulic hammer does not involve the noise of any escaping steam orother fluid, coupled with the fact that the region of the impacts isentirely enclosed, makes it possible to drive piles at locations, suchas near hospitals or residential areas, where heretofore theaccompanying noise has been highly objectionable.

The parts corresponding in function to those of Figs. 12, although shownin somewhat simplified form in Fig. 3, are identified by the samereference characters. Here the valve chamber 40 is shown as containing areciprocable piston type valve piece 54, operated if desired as by camfollowers in the form of rollers 55, 56, which are adapted to be engagedrespectively by the down-stroke cam 45' and the upstroke cam 44', thesecams being supported for example respectively by rods 57 and 53 mountedon the ram 13.

The valve piece 54 is shown in Fig. 3 in its central or dead centerposition and is about to be thrust to the right to admit liquidfromconnection 37 to the upper part of the cylinder for starting thedown-stroke. When the piston is about to start its upstroke, it will beunderstood that the cam follower 56 will engage cam 44' for thrustingthe valve to the left, allowing liquid from above the piston to beforced out through connection 38.

As shown in Fig. 3, the inlet connection 37 may have connected thereto ashock absorbing accumulator 59. This may be of any suitable known typeand preferably one which is capable, in so far as possible, ofwithstanding for prolonged periods, such hydraulic shocks as same mayreceive, and to cushion the eifect of such shocks in the hydraulicsystem, as above explained.

The hydraulic fluid, such as oil, may be contained in a tank 60 uponwhich may be mounted a high pressure hydraulic pump 61 driven by aninternal combustion engine 62 for pumping the oil through a connection63, through a spring-loaded relief valve 64, which has a connection 65back to the tank for returning liquid thereto in case excess pressuresare supplied to the outgoing connection 66.

A pilot pressure-operated unloading relief valve is indicated at 67 forpermitting return to the tank of excess 7 pressurized liquid in theline68 at a point beyond a clfeck valve 69. Another hydraulic accumulator.7'0fis c6 cted to the line 6 8 as may. also be a pressure gauge as at71'. 7

Finally the pressurized liquid may pass throughaquickopeninghammer-operated valve as at 72 and thence to the supply connection 37.running to the hydraulic hammer. A manually operable bleed-off valve 73may be locatedbetween the connection 37 and the tank 60.

The return connection 38 from the hydraulic hammer may communicatedirectly into the tank 60.

It will be understood that various features of the invention may be usedin hydraulic hammers of forms which are not necessarily of thedifferential type. Also the hammerslaccording tothe invention areadapted to be telescop'edwithin and enclosed by pile shells of certaintypes adaptedto be driven directly without using a pile core, :the termscore and core assembly as used herein are intended to apply to suchshells and the like aswell as to members more strictly referred to aspile cores.

As shown in Fig. 5, it will be noted that the hammer is substantiallyfully contained within the confines of the pile core and shell withoutthe necessity of increasing the sizes of the upper portions thereofbeyond the usual normal sizes. By the normal size of the upper end ofthe core is meant that same is either straight sided or has no'more thanthe usual slight taper, such as the taper which tapered pile shellscustomarily have, but not a bulging upper end such as disclosed in theabove-mentione'd patent to E. A. Smith No. 2,723,532.

Although certain particular embodiments of the invention are hereindisclosed for purposes of explanation, various further modificationsthereof, after study of this specification, will be apparent to thoseskilled in the art to which the invention pertains. Reference shouldaccordingly be had to the appended claims in determining the seopeof theinvention.

What is claimed and desired to be secured by Letters Patent is:

I. A hydraulically operated hammer for driving piles and the likecomprising in combination: a cylinder and differential piston and pistonrod assembly; a ram; means compressible in the'direction of the strokeof the piston for yieldably connecting the piston rod and ram; means forconstantlymaintaining hydraulic pressure surrounding the pistonrod andin under the piston during the operation of the hammer; a valve forcontrolling the admission and exhaust of liydraulic pressure above thepiston; valve operating means; and means connected to and operative inresponse to movements of the ram to actuate said operating means andthereby operating said valve to admit hydraulic pressure above thepiston substantially at the start of each downstroke thereof, and torelease such hydraulic pressure from above said piston at substantiallythe termination of each such downstroke.

2. A hydraulically operated hammer comprising in combination: acylinder, piston and piston rod assembly; a ram; spring meanscompressible in the direction of the stroke of the piston for yieldablyconnecting the piston rod and ram; a valve for controlling the admissionand exhaust of hydraulic pressure to the piston; valve operatingmcangand means operatively connected to and acting in response tomovements of the ram to actuate said operating means and therebyoperating said valve to admit hydraulic pressure to the pistonsubstantially at the start of each work stroke thereof and to releasesuch hydraulic pressure from said piston at substantially thetermination of each such work stroke.

3. A hydraulically operated hammer comprising in combination; acylinder, pistonand piston rod assembly;

a 'ra'mftwo springs compressible in'the direction of the.

stroke of the piston vfor yieldably connecting the piston ro d an'd ram;one, l0f said springs being positioned 'to become compressed'when theramfat a time near the end' of its working stroke, continues its,movement after, the. piston stops, the other of said springs beingpositioned piston substantially at the start. of each Work strokevthereof and to release such hydraulic pressure from said piston atsubstantially the termination of each such work stroke.

41A hydraulically operated hammer comprising in combination: alcylinder,piston and piston rod assembly; a ram; two means compressible in thedirection of the stroke of the piston for yieldably connecting thepiston rod and ram; one of said means being positioned to be compressedto allow the rod and ram to move toward each other, and the other ofsaid means being positioned to be compressed to allow the rod and ram tomove in a direction'further away from each other; a valve forcontrolling the admission and exhaust of hydraulic pressure to thepiston; valve operating means; and means operatively connected to andacting in response to movements of the ram to actuate said operatingmeans and thereby operating said valve to admit hydraulic pressure tothe piston substantially at the start of each work stroke thereof and torelease such hydraulic pressure from said piston at substantially thetermination of each such work stroke.

5. A hydraulically operated hammer comprising in combination: acylinder, piston and piston rod assembly;

' a ram; means for yieldably connecting the piston rod and ram; a valvefor controlling the admission and exhaust of hydraulic pressure to thepiston; valve operating means; and means operatively connected to andacting in timed relation to the movements of the ram to actuate saidoperating means and thereby operating said valve to admit hydraulicpressure to the piston substantially at the start of each work strokethereof and to release such hydraulic pressure from said piston atsubstantially the termination of each such work stroke of the piston,said yieldable means allowing overtravel of the ram as comand the likecomprising in combination: a cylinder, piston andpiston rod assembly; aram; means compressible in the direction of the strokes of the pistonfor yieldably I connecting the piston rod and ram; a valve forcontrolling theadmission and exhaustrespcctively of hydraulic pressureto the piston on the downstrokes and upstrokes thereof; and meansoperative in timed relation to the movements of the ram to actuate saidvalve to admit hydraulic pressure to the piston substantially at thestart of each downstroke thereof and to release such hydraulic pressurefrom said pistonsubstantially at the termination of eachsuch downstrokeof the piston, said compressible means allowingover-travelof the ram onits downstrokes and upstrokes as compared with the travel of the piston.

8. A hydraulically operated hammer and pile driving assembly, comprisinga hollow core having an upper portion,of. normal.size,.a differentialpiston and piston rod assemblyand a ram, all contained within andsurrounded by said .core, .thecore being adapted to be surrounded inturn by apil e, shell tobe driven by the impacts of the ram 'in thecore.

9. The combination comprising a hydraulically operated pile drivinghammer including a cylinder, a hydraulically operated piston and pistonrod assembly, a ram connected to the piston rod, and a shell-like memberadapted to be driven by the hammer and containing and surrounding allsaid parts.

10. A hydraulically operated hammer for driving piles and the like,comprising in combination: a hydraulic system including a cylinder,piston and piston rod; a cam; and means yieldably associating thehydraulic system with said ram to actuate the latter, such yieldabilityat least substantially at the time when the piston is approaching theend of its stroke in and with respect to the cylinder, permittingfurther travel of the ram and completion of its stroke withoutdestructive shock on the hydraulic system.

11. A hydraulically operated hammer for driving piles and the like,comprising in combination: a hydraulic system including a cylinder,piston and piston rod and valve means for admitting and dischargingliquid with respect to the cylinder for operating the piston; a ram; andcompressible means for yieldably associating the ram with said system,said compressible means allowing over-travel of the ram as compared withthe movement of the piston with respect to the cylinder.

No references cited.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,798,363 July 9, 1957 John T. Hazak et al.

; It is hereby certified that error appears in the printed specificationbf the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column '7, line 22, for "Fig. 5" read Fig. 4 column 9, line 9, for "acam" read a ram Signed and sealed this 27th day of August 1957.

( L) Attest:

KARL AXLINE ROBERT c. WATSON Attesting Officer Conmissioner of Patents

